<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
    margin: 0;
    overflow: hidden;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    -o-user-select: none;
    user-select: none;
    }
    body {
        background: #F2F2F2;
    }
    #c {
        display: block;
        margin: 20px auto 0;
    }
    #info {
        position: absolute;
        left: -1px;
        top: -1px;
        width: auto;
        max-width: 420px;
        height: auto;
        background: #f8f8f8;
        border-bottom-right-radius: 10px;
        border:1px solid #ccc;
    }
    #top {
        background: #fff;
        width: 100%;
        height: auto;
        position: relative;
        border-bottom: 1px solid #eee;
    }
    p {
        font-family: Arial, sans-serif;
        color: #666;
        text-align: justify;
        font-size: 16px;
        margin: 0px 16px;
    }
    #github, #twitter {
      color:#3377ee;
      font-family: Helvetica, Arial, sans-serif;
      font-size: 14px;
      margin: 0 auto;
      text-align: center;
      text-decoration:none;
    }
    .center {
      text-align: center;
    }
    #net {
      text-align:center;
      white-space:nowrap;
      font-size:19px;
      background:rgba(0,0,0,0.1);
      padding:8px 12px;
      border-radius:8px;
      display:block;
      color:#888;
    }
    #net > span {
      color:#3377ee;
      font-family: Helvetica, Arial, sans-serif;
      font-size: 14px;
      display: block;
      margin: 0 auto;
      text-align: center;
      text-decoration:none;
    }
    a {
        font-family: sans-serif;
        color: #444;
        text-decoration: none;
        font-size: 20px;
    }
    #site {
        float: left;
        margin: 10px;
        color: #ff9900;
      border-bottom: 1px dashed #ccc;
      padding-bottom:3px
    }
    #site:hover {
        color: #ffaa11;
    }
    #close {
        float: right;
        margin: 10px;
    }
    #p {
        font-family: Verdana, sans-serif;
        position: absolute;
        right: 10px;
        bottom: 10px;
        color: #4099ff;
        border: 1px dashed #4099ff;
        padding: 4px 8px;
    }

    #new {
      width: 100%;
      text-align: center;
      font-size: 18px;
      font-family: Helvetica;
      margin-top: 12px;
    }

    #new a {
      font-size: 20px;
      color: #4099ff;
    }

    .bull {
      opacity: 0.3;
      margin: 0 6px;
      font-size: 14px;
    }



  </style>
</head>
<body>
  <canvas id="c"></canvas>

  <div id="info">
    <div id="top">
      <a id="close" href="">&times;</a>
    </div>
    <p>
      <br>- Tear the cloth with your mouse
      <br>
      <br>- Right click and drag to cut
      <br>
      <br>
      <br>
      <div class="center">
        <a id="github" target="_blank" href="https://github.com/dissimulate/Tearable-Cloth">GitHub</a>&nbsp;<!--span class="bull">&bull;</span>&nbsp;<a id="twitter" target="_blank" href="https://twitter.com/abro_oks">@abro_oks</a-->
    </div>
      <br>
    </p>
  </div>

  <!--div id="new">
    Wobble some <a target="_blank" href="https://codepen.io/dissimulate/details/dJgMaO">jelly</a> <span class="bull">&bull;</span>
    Check out my <a target="_blank" href="https://www.instagram.com/abro_oks/">instagram!</a>
  </div-->
  <script>

    document.getElementById('close').onmousedown = function(e) {
      e.preventDefault();
      document.getElementById('info').style.display = 'none';
      return false;
    };

    // settings

    var physics_accuracy  = 3,
        mouse_influence   = 20,
        mouse_cut         = 5,
        gravity           = 1200,
        cloth_height      = 30,
        cloth_width       = 50,
        start_y           = 20,
        spacing           = 7,
        tear_distance     = 60;


    window.requestAnimFrame =
        window.requestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
        window.mozRequestAnimationFrame ||
        window.oRequestAnimationFrame ||
        window.msRequestAnimationFrame ||
        function (callback) {
            window.setTimeout(callback, 1000 / 60);
    };

    var canvas,
        ctx,
        cloth,
        boundsx,
        boundsy,
        mouse = {
            down: false,
            button: 1,
            x: 0,
            y: 0,
            px: 0,
            py: 0
        };

    var Point = function (x, y) {
        this.x      = x;
        this.y      = y;
        this.px     = x;
        this.py     = y;
        this.vx     = 0;
        this.vy     = 0;
        this.pin_x  = null;
        this.pin_y  = null;
        
        this.constraints = [];
    };

    Point.prototype.update = function (delta) {
        if (mouse.down) {
            var diff_x = this.x - mouse.x,
                diff_y = this.y - mouse.y,
                dist = Math.sqrt(diff_x * diff_x + diff_y * diff_y);

            if (mouse.button == 1) {
                if (dist < mouse_influence) {
                    this.px = this.x - (mouse.x - mouse.px) * 1.8;
                    this.py = this.y - (mouse.y - mouse.py) * 1.8;
                }
              
            } else if (dist < mouse_cut) this.constraints = [];
        }

        this.add_force(0, gravity);

        delta *= delta;
        nx = this.x + ((this.x - this.px) * .99) + ((this.vx / 2) * delta);
        ny = this.y + ((this.y - this.py) * .99) + ((this.vy / 2) * delta);

        this.px = this.x;
        this.py = this.y;

        this.x = nx;
        this.y = ny;

        this.vy = this.vx = 0
    };

    Point.prototype.draw = function () {
        if (!this.constraints.length) return;

        var i = this.constraints.length;
        while (i--) this.constraints[i].draw();
    };

    Point.prototype.resolve_constraints = function () {
        if (this.pin_x != null && this.pin_y != null) {
            this.x = this.pin_x;
            this.y = this.pin_y;
            return;
        }

        var i = this.constraints.length;
        while (i--) this.constraints[i].resolve();

        this.x > boundsx ? this.x = 2 * boundsx - this.x : 1 > this.x && (this.x = 2 - this.x);
        this.y < 1 ? this.y = 2 - this.y : this.y > boundsy && (this.y = 2 * boundsy - this.y);
    };

    Point.prototype.attach = function (point) {
        this.constraints.push(
            new Constraint(this, point)
        );
    };

    Point.prototype.remove_constraint = function (constraint) {
        this.constraints.splice(this.constraints.indexOf(constraint), 1);
    };

    Point.prototype.add_force = function (x, y) {
        this.vx += x;
        this.vy += y;
      
        var round = 400;
        this.vx = ~~(this.vx * round) / round;
        this.vy = ~~(this.vy * round) / round;
    };

    Point.prototype.pin = function (pinx, piny) {
        this.pin_x = pinx;
        this.pin_y = piny;
    };

    var Constraint = function (p1, p2) {
        this.p1     = p1;
        this.p2     = p2;
        this.length = spacing;
    };

    Constraint.prototype.resolve = function () {
        var diff_x  = this.p1.x - this.p2.x,
            diff_y  = this.p1.y - this.p2.y,
            dist    = Math.sqrt(diff_x * diff_x + diff_y * diff_y),
            diff    = (this.length - dist) / dist;

        if (dist > tear_distance) this.p1.remove_constraint(this);

        var px = diff_x * diff * 0.5;
        var py = diff_y * diff * 0.5;

        this.p1.x += px;
        this.p1.y += py;
        this.p2.x -= px;
        this.p2.y -= py;
    };

    Constraint.prototype.draw = function () {
        ctx.moveTo(this.p1.x, this.p1.y);
        ctx.lineTo(this.p2.x, this.p2.y);
    };

    var Cloth = function () {
        this.points = [];

        var start_x = canvas.width / 2 - cloth_width * spacing / 2;

        for (var y = 0; y <= cloth_height; y++) {
            for (var x = 0; x <= cloth_width; x++) {
                var p = new Point(start_x + x * spacing, start_y + y * spacing);

                x != 0 && p.attach(this.points[this.points.length - 1]);
                y == 0 && p.pin(p.x, p.y);
                y != 0 && p.attach(this.points[x + (y - 1) * (cloth_width + 1)])

                this.points.push(p);
            }
        }
    };

    Cloth.prototype.update = function () {
        var i = physics_accuracy;

        while (i--) {
            var p = this.points.length;
            while (p--) this.points[p].resolve_constraints();
        }

        i = this.points.length;
        while (i--) this.points[i].update(.016);
    };

    Cloth.prototype.draw = function () {
        ctx.beginPath();

        var i = cloth.points.length;
        while (i--) cloth.points[i].draw();

        ctx.stroke();
    };

    function update() {
        ctx.clearRect(0, 0, canvas.width, canvas.height);

        cloth.update();
        cloth.draw();

        requestAnimFrame(update);
    }

    function start() {
        canvas.onmousedown = function (e) {
            mouse.button  = e.which;
            mouse.px      = mouse.x;
            mouse.py      = mouse.y;
            var rect      = canvas.getBoundingClientRect();
            mouse.x       = e.clientX - rect.left,
            mouse.y       = e.clientY - rect.top,
            mouse.down    = true;
            e.preventDefault();
        };

        canvas.onmouseup = function (e) {
            mouse.down = false;
            e.preventDefault();
        };

        canvas.onmousemove = function (e) {
            mouse.px  = mouse.x;
            mouse.py  = mouse.y;
            var rect  = canvas.getBoundingClientRect();
            mouse.x   = e.clientX - rect.left,
            mouse.y   = e.clientY - rect.top,
            e.preventDefault();
        };

        canvas.oncontextmenu = function (e) {
            e.preventDefault();
        };

        boundsx = canvas.width - 1;
        boundsy = canvas.height - 1;

        ctx.strokeStyle = '#888';
      
        cloth = new Cloth();
      
        update();
    }

    window.onload = function () {
        canvas  = document.getElementById('c');
        ctx     = canvas.getContext('2d');

        canvas.width  = 560;
        canvas.height = 350;

        start();
    };







  </script>
</body>
</html>